Recently, multi-layered interconnection structures have been increasingly used to support trends related to the miniaturization and high integration of semiconductor devices. Copper (Cu) interconnections that possess low electrical resistivity have been used for the purpose of preventing propagation delay of signals that flow through the interconnections. The Cu interconnections may be produced through a damascene process.
Cu interconnections formed using damascene processes are buried in very fine structures where voids may be formed therein. A void inside the Cu interconnection adversely affects the reliability of the Cu interconnection, and can cause the disconnection of the Cu interconnection and/or an increase in the interconnection resistance. The detection of the void formed inside the Cu interconnection is thus highly desirable (see Japanese Patent Application Publication No. JP-A-H8-255818).
Conventional void detection methodologies include potential contrast failure detection and optical measurement detection. As it regards potential contrast failure detection, using this approach electron beams are irradiated on the substrate surface to detect the discharge volume of the secondary electrons, which depends on the conduction state of the Cu interconnection such that a void that is formed inside the Cu interconnection is detected. Referring to FIG. 1, in cases where a void 10 is formed inside a Cu interconnection 13 in a SiO2 film 18 and acts to interrupt the conduction state of the Cu interconnection 13 completely, that is, it is brought into the electrically open state, the void 10 may be detected.
Referring to FIG. 2, as it regards optical measurement, when a void 10 is exposed to the surface of the Cu interconnection as shown in FIG. 2, it may be readily detected using optical measurement detection. A detection problem is presented when a void 10 is formed inside a Cu interconnection 13 and the conducting state of the Cu interconnection 13 is not completely interrupted. In this case, the void 10 cannot be detected by potential contrast failure detection. Moreover, as the void 10 is not exposed to the surface of the Cu interconnection 13, it also cannot be detected through the use of optical measurement detection. Consequently, a semiconductor device having an undetected void 10 as shown in FIG. 3 may be defective in a final reliability evaluation due to stress migration and electro-migration caused by the void 10. The ability to detect voids such as is shown in FIG. 2 is thus highly desirable.